1. Field of the Invention
The invention is generally related to the lubrication of wire ropes and more particularly to the in situ lubrication of wire ropes on cranes.
2. General Background
Wire rope is a flexible, tough, complex, and versatile mechanical power transmission member made up of numerous individual wires. During normal operation these wires are subject to torsion, bending, tension, and compression stresses. To achieve maximum performance and life, lubrication of the wire rope structure must be maintained so that coordinated sliding action between individual wires permits most favorable distribution of these stresses. Good lubrication offers protection against corrosion and minimizes metal-to-metal contact between individual wires while reducing wear on the rope and on the drum and sheaves over which it operates.
Wire rope used on cranes typically is pre-lubed by the manufacturer with a base lubricant. Typically, this is a thick lubricant with very high viscosity (10 to 30,000 SUS) that provides good protection during storage. However, to perform properly, a wire rope must also be field lubricated periodically. For this post-lube application a lighter viscosity oil such as 150 SUS must be applied to the rope because, during operation, tensions in the rope and pressure encountered while operating over sheaves and drums all work toward forcing the original lubricant to the rope surface. New oil is needed to counteract that action.
Field lubrication of wire rope has traditionally been done by one or more methods. A stationary device may be positioned such that it surrounds the wire rope in a continuous bath and lubricates the rope as it moves through the device. Lubricant may be dripped or poured on the wire rope and the excess then wiped off. Lubricant may be swabbed or painted on the wire rope. Some of these operations must be done manually.
The nature of large cranes, especially those used on derrick barges for offshore work, precludes the use of most of the current lubrication methods for several reasons. Large cranes have miles of wire rope, some of which moves in excess of one hundred feet per minute. Cranes achieve a mechanical advantage by the use of multi-sheaved wire rope block assemblies. This creates numerous closely spaced wire loops, which make in-situ lubrication very difficult. Conventional wire rope lubricators are not well suited to address a plurality of closely spaced wires due to the large size of the lubricators and their inability to operate in hands-off mode (they require constant attention and adjustment). Current lubrication devices are not designed for a plurality of wire ropes like the ones present in a multi-sheaved wire rope assembly. Current lubrication devices can not be installed and maintained in inaccessible locations like the boom of a derrick crane or the main block of a multi-sheaved hoist. Current lubrication devices are typically stationary but rely on relative motion between wire and lubricator. One such device is the pressurized clamshell lubricator. Pressurized clamshell lubricators have a split-housing chamber with round openings in their axial direction. The wire rope is fed through the axial openings and bathed in lubricant. Current clamshell units have disadvantages. They require a lot of time to set up and take down. Also, they must be removed during normal crane operation. Bathing the wire rope in lubricant tends to use excess lubricant that is not required. This wastes lubricant and causes pollution problems. In a crane, portions of the wire rope are stationary once installed. Thus, a stationary lubrication device is ineffective for those portions of wire rope.
It can be seen that the current state of the art does not address all needs in lubricating wire rope on cranes.
The invention allows for lubrication of the entire length of wire rope in a crane after wire is installed. This is done with the various devices that are described herein. Spray nozzles may be permanently mounted to the multi-sheaved wire block assemblies. A controller and oil supply located near the base of the crane are used to control and deliver oil to the spray nozzles. A telescopic spray unit is used to lubricate the vertical stationary wire rope. A crawler that rides on the wire rope is used to lubricate the stationary wire rope between the anchor point and the first sheave of the block assembly. Improved clamshell units are used to lubricate the wire rope between the drums storing wire rope and the first sheave.